"For the first time, under the terms of this constitution, every Fijian has a voice and I am assured that voice will be heard next year without hindrance," he said.

"It is the constitution we had to have for us to join the ranks of the world's great democracies."

Fiji's interim prime minister, Frank Bainimarama, has described the new constitution as a "blueprint for democracy", marking a "new beginning" for the island nation.

Commodore Bainimarama says the 2013 constitution will make Fiji democratic.

"The 2013 Fijian constitution enshrines principles that are at the heart of all the great liberal democracies...an independent judiciary, a secular state and a wide range of civil, political and social-economic rights," he said.

During the ceremony at Government House in Suva, both the president Ratu Epeli Nailatikau and interim Prime Minister Frank Bainimarama dismissed claims of rights restrictions in the document.

The new constitution was drawn up by the military regime after it scrapped a draft supplied by a specially selected constitutional committee.

Our reporter in Suva, Samisoni Pareti, says about 30 to 40 people from pro-democracy movements and some political parties were involved in the protest.

"When the police arrived to break up the protest, they took about 14 men and women, mostly young people, who were holding placards, put them in a bus and took them over to the police headquarters to be charged," he said.

He says the protesters were released after about an hour of detention and were told it's unlawful for them to be holding placards that were denouncing the new constitution.

Rights groups raise concern

Rights groups have also criticised provisions which grant legal immunity to those behind the 2006 coup.

Human rights organisation Amnesty International has expressed concern at the detention of demonstrators in Fiji.

Amnesty International spokesperson Michael Hayworth has told Radio Australia's Pacific Beat everyone has the right to demonstrate and the incident is part of a pattern of disturbing behaviour by the interim government in Fiji.